The invention concerns a switching element for a valve train of an internal combustion engine, preferably for valve deactivation, said switching element comprising an outer element and an inner element that is arranged for axial displacement in a bore of the outer element, each of the outer element and the inner element comprising at least one reception aligned to each other in an axially distant relative position which is achieved through a lost motion spring, at least one piston being arranged in at least one of the receptions for sliding toward the other of the receptions to couple the inner element to the outer element in said relative position, and a high-position stop for defining said relative position being arranged between the inner and the outer element.
A switching element of the pre-cited type is disclosed in the generic prior art document DE 199 15 531 which shows a switchable cam follower for a tappet push rod drive. The high-position stop for defining the relative position is formed by a piston-like element arranged in the inner element. This piston-like element projects radially outward into a longitudinal groove of the outer element. In the axially extracted state of the inner element from the outer element, the piston-like element abuts against one end of the longitudinal groove. The purpose of this is to create an aligned arrangement of a coupling bore made in the outer element for a piston arranged in the inner element for achieving coupling.
A drawback of this prior art is that an adjustment of lash in the coupling is relatively complicated and cost-intensive. It is clear that the reception (coupling bore) in the outer element for receiving the piston must be configured with a slight lash relative to the outer peripheral surface of the piston. This lash and the high position differ from switching element to switching element due to fabrication conditions. The relatively wide range of variance of this mechanical idle travel in switching elements is, however, undesirable.
Therefore, to keep the coupling lash or its variance within acceptable limits, pistons to be used for coupling are sorted into groups. This procedure is extremely expensive from the point of view of fabrication and measuring techniques. For example, the switching elements are first completely mounted, the lash is then measured following which, the switching elements are dismounted again and an appropriate piston is then chosen for coupling. It is equally conceivable to group the high-position stops provided on the longitudinal grooves of the outer elements.
If, as disclosed in DE 42 06 166, two pistons are used for coupling, the stop measures described above prove to be quasi impossible. The aligned position of the coupling bores that are situated diametrically opposite each other in the inner element is realized by the contact of the two axially displaceable parts of the switching element on the base circle of the cam. From the point of view of fabrication and measuring techniques, the adjustment of the lash of the coupling is implemented in an extremely complicated and expensive manner by a pairing of corresponding switching elements (in this case, cup tappets to cam pairs or cam shafts). Under certain circumstances, a too large variation of lash will have to be allowed.
It is an object of the invention to provide an improved switching element of the pre-cited type in which the aforesaid drawbacks are eliminated by simple measures.
This and other objects and advantages of the invention will become obvious from the following detailed description.
The invention achieves the above objects by the fact that the high-position stop is made as a separate element of variable thickness such as a disk or a circlip that is fixed on one of the outer element and the inner element and cooperates with a stop surface of one of the inner element and the outer element. In a particularly advantageous embodiment of the invention, coupling is achieved by two pistons that extend diametrically opposite each other in the reception of the inner element, which reception is made as a radial bore, said pistons being aligned to the receptions of the outer element in the relative position.
The separate element of the invention disposed, for example, in the bore of the outer element, forms a simple, tilt-free and adjustable high-position stop. The initially described drawbacks are thus eliminated by simple measures. During a mounting of the switching element (disk, circlip or the like), different thicknesses of the separate element can be chosen to adjust the mechanical idle travel of the at least one coupling element (preferably two) relative to the reception in which it is arranged. This means in other words, that in the axially extracted state of the inner element from the outer element, the annular high-position stop enables the axes of the receptions and the axes of the pistons to be aligned or adjusted to one another for achieving coupling. In place of a variation of the thickness of the separate element, the height of the inner element with its end face may also be varied.
The scope of protection of the invention extends explicitly to all types of switching elements in valve trains such as cam followers in tappet push rod drives, cup tappets and support elements for finger levers. The invention extends likewise to switching elements that are installed directly in lever-type cam followers. The switching elements may be designed for complete de-actuation or for switching to different cam lifts.
According to a further feature of the invention, the separate element serves at the same time as a safety device against loss and for transportation. In this way, additional securing measures that may possibly have to be removed prior to mounting the switching element in the internal combustion engine can be dispensed with.
The invention will now be described more closely with reference to the appended drawing.